The present invention relates to new and novel silane chelating agents which can be immobilized on inorganic solids and used to chelate metals from solution.
It is well-known in the art to treat inorganic solids with hydrolyzable organosilanes to bond the organosilanes to the inorganic solid surfaces. For example, British Pat. No. 1,530,039 published Oct. 25, 1978 and assigned to the British Petroleum Company Limited, shows the use of polyamines bonded to inorganic solids by the use of an organosilane coupling agent. The organosilane coupling agent is described preferably as alpha-chloropropyl-trimethoxysilane and the polyamine s N(CH.sub.2 CH.sub.2 NH.sub.2).sub.3. Leyden, et al., Anal. Chem., 47(a), pp. 1612 to 1617, August 1975, shows the use of aminoalkyltrimethoxysilanes as treatments for silica gel to give a silica having aminoalkylsilyl groups on the surface which are subsequently derivatized to the corresponding dithiocarbamate to give chelating groups on the surface of the silica.
Pleuddemann, U.S. Pat. No. 4,071,546, issued Jan. 31, 1978, prepared carboxymethyl containing polyaminosiloxanes which were bonded to siliceous supports which were subsequently used as metal chelating agents and Hancock et al., in U.S. Pat. No. 4,203,952, issued May 20, 1980 and assigned to the British Petroleum Company, shows the use of silane coupling agents to bond various amine functional chelating compounds to inorganic solids.
Finally, G. D. Schucker et al., in U.S. Pat. No. 3,886,080, issued May 27, 1975 shows the use of silane coupling agents to immobilize certain chelating agents on inorganic solids. Specifically, the compound 8-hydroxyquinoline is shown as one of the chelating agents that can be bound to inorganic solids by their method.
What has been discovered and disclosed herein is a new and novel means by which to attach the 8-hydroxyquinoline chelating agent to the surface of inorganic solids which results in a new immobilized chelating substance which has durability on the inorganic solid substrate thereby giving the chelating agent extended chelating capacity.
Percolation of dilute heavy metal ion solutions through silylated silica has been used as an analytical method for concentrating the metal ion for estimation by X-ray fluorescence (D. E. Leyden, M. L. Steele and B. B. Jablonski, Anal. Chem. Acta, 100 549 (1978)). In these methods, amine functional silanes were used to bond chelating agents to the silica surface. Materials such as (CH.sub.3 CH.sub.2 O).sub.3 Si(CH.sub.2).sub.3 NH.sub.2 and (CH.sub.3 O).sub.3 Si(CH.sub.2).sub.3 NH(CH.sub.2).sub.2 NH.sub.2 have been the preferred silylating agents and these materials give almost quantitative yields when used as chelating agents themselves. Capacity for metal ions is proportional to surface area of the filler. These hydrolyzed hydrophilic silanes when deposited under mild conditions on siliceous surfaces are not tightly bonded to the surface through the surface silanols. Siloxane bonds formed between the coupling agent and the siliceous surface are hydrolyzable and if the hydrolyzed hydrophilic silane is a monomer or an uncrosslinked oligomer, the coupling agent is displaced relatively easily from the surface. Crosslinking such monomers or oligomers while on a silica surface, such as by heating, is not a useful method of imparting durability to the treated surface since for the metal ion removal application, the reactivity of the metal ions is reduced or lost.
The hydrophilic diamine group on a silica surface becomes even more hydrophilic in acid solutions such as are used to elute metals from chelate-silylated surfaces.
Among those known useful chelating agents, it is believed that the 8-hydroxyquinoline derivative is probably preferred because it has a high capacity for chelating more types of metals (see U.S. Pat. No. 3,886,080, Tables I-X).
Further, as it has already been pointed out by Schucker, supra, inorganic solid substrates for immobilization of the chelating agents are preferred over that of organic carriers because the inorganic carriers are biologically stable; they do not tend to swell or shrink with changing conditions of pH and, such compositions can be sterilized without degradation (see Column 2, line 15 et seq. of Schucker).
It would thus appear that it would be desirable to have an 8-hydroxyquinoline chelating agent durably bonded to an inorganic solid so that one could enjoy the combined benefits thereof and overcome prior art disadvantages. The present invention does overcome the disadvantages of the prior art immobilized chelating agents.
It is one object of this invention to provide novel silicon-containing chelating agents which are useful for removing heavy metal ions from solutions.
It is another object of this invention to provide a new process for preparing the novel chelating agents.
It is yet another object of this invention to provide immobilized chelating agents which have durability in use.
These and other objects will become obvious after consideration of the following disclosure and claims.